两相合金中的水静应力对宏观流变行为和微观断裂机制的影响

EFFECT OF HYDROSTATIC STRESSES ON MACRO-FLOW BEHAVIOUR AND MICRO-FRACTURE MECHANISM OF TWO PHASE ALLOYS

理论分析和有限元数值结果表明,由软、硬两相相互作用而产生的水静拉伸和压缩应力使两相合金中软质相硬化而硬质相软化。这种软化和硬化倾向与相连续性无关。软化、硬化程度随相含量的增加而下降。组分相的硬化和软化效应对两相合金的流变行为有着重要影响,是使用混合律估计双相合金流变应力失效的一个重要原因。本文还给出相间应力三轴性(定义为水静应力与等效应力之比)的分布形态。为揭示双相合金的微观断裂机制提供了一个清晰的物理图景。

The aspects of hydrostatic pressure and tension stresses developed as a re- sult of the interaction between hard and soft phase to maintain compatibility are represented for two-phase alloy with different microstructures. It has been theoretically proved that the stress triaxiality, defined as the ratio of the hy- drostatic stress to the effective stress (σ_H/σ_e), causes hardening or softening of the component phases. The average hydrostatic tension and pressure stresses in soft and hard phases developed during monotonic loading make the soft phase hardaning and hard phase softening, which are independent of phase continuity The extent of the hardening and softening effects increases with the increase of the strength ratio of the hard phase to soft one and the size of the par- ticle phase, and decreases with the increase of the phase content. The harden- ing or softening effect of the in situ constituents has important influence on flow stress of the composites and is one of the important reasons of the break- ing of the law of mixtures in predicting the flow stress of the composites based on that of the component phases in bulk. The feature of stress triaxia- lity distributions in microstructure scale also provides an explicit physical pic- ture to reveal the micro-fracture mechanisms of the two-phase alloys.